Diamond turns to government and religion, exploring how they arose in different ways around the world. He begins by dividing societies into four categories: band, tribe, chiefdom, and state.

Bands are small groups of up to eighty people related by family ties. They live and work together without much connection to anyone outside their group. Bands tend to be egalitarian, without class structure and with informal leadership. Very few people still live in bands today.

Tribes form the second smallest kind of society. For the purposes of the political discussion in this book, a tribe is defined as a group made up of hundreds of settled people organized into political units at the level of a village or cluster of villages. Tribes usually consist of more than one family group, each of which has its own land. Tribal governments are still relatively egalitarian, involving communal decision making and no formal class structure, although some tribes have chiefs with limited power. Like bands, tribes exist relatively rarely as political groups today. Most former tribes are incorporated into a larger political structure.

The third kind of political organization, the chiefdom, no longer exists independently today. However, chiefdoms were very common from about 7,500 years ago until the colonial period. They consisted of groups of several thousand to tens of thousands of people who were ruled by a chief with exclusive control over the group. The chief’s office was formal, inherited, and permanent. Society was arranged into chief and commoner classes.

Chiefdoms incorporated systems of taxation and produced varying results for their inhabitants. Some chiefdoms provided a better life than people could achieve individually. Others worked as kleptocracies, merely transferring wealth from the common people to the upper classes. Leaders kept power by arming elite groups, redistributing wealth in popular ways, maintaining social order, or promoting institutionalized religion to justify themselves.

Today the most common and influential kind of political organization is the state. States arose for the first time by around 3700 BCE and eventually grew to cover almost all the world’s habitable surface. States are larger than chiefdoms, uniting up to more than a billion people under a single political system. They usually contain more than one major city, build large public works, accumulate taxes, and house large numbers of people who are not food producers. States have highly centralized, far-reaching control; they incorporate stratified bureaucracy, codify laws, and develop penal and justice systems. Early states had hereditary rulers and centralized religious systems. They diverged from chiefdoms in that they incorporated multilingual and multiethnic societies. Later states have often adopted nonhereditary leadership.

Diamond points out that, over the past 13,000 years, human political organization has replaced small societies with larger ones (with a few exceptions). States have better weaponry than smaller political organizations do, and most states actively cultivate some kind of patriotism or religious identification, or both, into their members.

States have come into being separately in many separate societies, on many separate continents, in environments where no other states had existed. Diamond examines several theories about why states arise, and he concludes that people do not form states merely out of logical, far-sighted thoughts about personal welfare. Instead, evidence shows that members of band and tribes often resist being incorporated into states. Similarly, Diamond rejects the idea that states may have been built to maintain large public works projects such as irrigation systems. He thinks people must have been well on their way to forming states before they could have conceived of such projects.

Diamond believes that larger, denser population sizes demand more complex political organization than do smaller, less dense populations. Because of this, he thinks food production stimulates complex political organization. Producing food causes population growth, which creates a pressure for people to organize. This allows people to work together better and produce more food, which in turn stimulates further population growth. Food production also creates other conditions necessary for chiefdoms and states. For instance, it requires people to adopt sedentary lifestyles.

Food production clearly makes larger societies possible, but Diamond also claims it makes them inevitable. Larger populations create situations in which people have to interact with unrelated strangers, so people are forced to create formal customs to resolve conflicts. Communal decision making becomes increasingly difficult as populations grow, so increasingly powerful leaders become necessary.

As societies compete, larger societies tend to conquer and incorporate smaller ones if they can. Smaller societies rarely decide to merge with larger ones of their own free will. Rather, they do so when forced or when threatened by an outside force. Wars, therefore, tend to cause societies to merge but only when populations are already relatively large. In diffuse populations, defeated survivors of conflict can simply move farther away from their enemies. Where populations are higher, conquered groups have nowhere to flee, and they are more likely to be killed or absorbed into the conquering population.